1. Field of the Invention
This invention relates to a method and an apparatus for producing a fasciated yarn with a specific structure, a core portion of which has a true twist of the same direction as that of surface fibers entangling around the core portion, and for producing a two-folded yarn consisting of the above-mentioned yarns in one process.
2. Description of the Prior Art
Fasciated yarn spinning is a process in which a ribbon-like fiber bundle is continuously introduced into an air twisting nozzle and false-twisted by a vortex generated within a yarn passage in the air twisting nozzle, thereby causing edge portion fibers of the fiber bundle to entangle with a core portion thereof to form a yarn having a mechanical strength sufficient for practical use, though the core portion is of a substantially twistless structure.
The mechanism for forming the fasciated yarn is as follows. The ribbon-like fiber bundle has a plurality of "free end fibers" in its edge portion. "Free end fiber" means a fiber with one end embedded in the core portion of the fiber bundle and the other end free from constraint from any other fibers. When the fiber bundle is subjected to the vortex, both the core portion and the free end fibers are rotated. The free ends remain straight in the early period of the twisting operation, therefore are finally wound onto the core portion with less number of twists than that of the core portion itself. During the untwisting operation after the twisting operation, the core portion of the fiber bundle is completely untwisted to its original state, i.e., zero twist. However, the free end fibers are overly untwisted past the zero twist point to an extent corresponding to the difference between the twist numbers of the core portion and the free end fibers at the end of the prior twisting operation and entangle around the twistless core portion to form a fasciated yarn.
Such fasciated yarn can be produced at a high rate by utilization of an air twising nozzle generating a high rotational speed vortex.
However, a conventional roller drafting system utilized for preparing the fiber bundle cannot endure a speed of processing as high as that of the above-mentioned fasciated yarn spinning, because the aprons in the drafting system would be easily damaged in a short time period.
In an entirely different area, there has been prevailed open-end spinning. In open-end spinning, a fiber opened from a sliver is fed onto a collecting surface of a rotating drum rotor to form fiber layers by the action of centrifugal force exerting on the open fibers. The fiber layers are then continuously drawn off from the collecting surface as a fiber bundle while being imparted with a true twist due to the rotation of the drum rotor during the drawing-off operation.
In open-end spinning, since the roller drafting system can be omitted, the afore-said problem is diminished. Moreover, this spinning system had also an advantages of high rate production due to light weight of the drum rotor. However, open-end spinning is not suitable for producing a thinner yarn because the yarn may break by excessive tension caused by the centrifugal force.